Final answer:
The story's primary purpose is to entertain while it also informs or educates the audience about the complexities of living with a family member who is a veteran with substance abuse issues, using the PIE components of storytelling.
Step-by-step explanation:
The story of a teenage boy learning to understand and live with his alcoholic Vietnam War veteran father likely has multiple purposes, but primarily, it seems to aim to entertain the reader while also providing insight into the challenges faced by families of veterans with substance abuse issues. The acronym PIE stands for Persuade, Inform, and Entertain, which are common purposes in writing. Considering the narrative described engages the audience with its storytelling while addressing serious social issues suggests that the piece of writing has a dual purpose: to entertain and to inform or educate. Therefore, among the given options, the most suitable answer would be 'Author's Purpose: To entertain, PIE: Persuade, Inform, Educate' aligning with option D.